The invention relates to a speed brake for aircrafts according to the preamble of the patent claim 1.
A speed brake is a flap on a vehicle which flap can be extended into the air stream and which increases the flow resistance of the air and thus serves as brake. The resistance increase caused by a speed brake can take place by increasing the front area or by increasing the drag coefficient cd. Hereby, the induced drag is increased. Since downstream of the speed brakes, the laminar flow stalls at the airfoil, in addition, the lift decreases.
Speed brakes are used for aircrafts to reduce the airspeed (at a higher angle of attack), to increase the rate of descent or to reduce the landing run during landing. In case of military aircrafts, the speed brake is also used for tactical maneuvers (e.g. Cobra maneuver) or to reduce the speed during a nosedive (dive brake).
The brake flaps of aircrafts are extended mechanically or hydraulically from the upper or lower side of the airfoils but also from both sides. Also, in case of combat aircraft, brake flaps are used that extend from the bottom of the fuselage or the side walls of the fuselage. In most cases, the flap itself is curved and adapted to the fuselage contour. FIG. 1 schematically illustrates a military aircraft F in a side view. In the region of the airfoil T there is a speed brake in the form of an extendable flap 1.
In the retracted state, the flap 1 adapts to the outer contour of the aircraft F.
One problem is that downstream of the flap, strong air vortices develop which are also known as Karman vortex street (FIG. 2). Downstream of the cylinder 1a, which lies transverse to the flow, the oppositely rotating vortices 2 are shown which depart alternately from the one side and the other side of the body 1a. The flow downstream of the speed brake 1 behaves similarly as schematically illustrated in FIG. 3.
These vortices 2 result in pressure fluctuations (pressure vibrations) which can cause not only the speed brake itself to vibrate but also, in particular, the areas of the aircraft downstream of the speed brake and can significantly reduce the durability of the same or can even destroy them within a short time if the narrowband vibration gets into resonance with the component. FIG. 3 illustrates schematically in picture 3 the alternating pressurization on a vertical stabilizer arranged downstream of the speed brake 1.
Exemplary embodiments of the present invention provide a generic speed brake that can reduce or prevent such pressure fluctuations.
The speed brake according to the invention for aircraft is in the form of a flap that is extendible into the air flow for increasing the flow resistance of the air and is characterized in that an extension is attached on the upper side of the flap on one side with respect to the center line of the flap in such a manner that the extension extends in the retracted state of the flap along the flow direction of the air.
In the extended state, the extension according to the invention changes the outflow of the vortices on one side and thus prevents the symmetrical and alternating departure of equally large vortices. This reduces the amplitude of the pressure fluctuations downstream of the flap and reduces the risk of resonance.
Thus, the fundamental idea of the invention is to modify the flap on its side facing the flow in such a manner that the air flow no longer runs symmetrically over the flap as this is the case in the prior art, but asymmetrically, whereby the desired effect of a symmetrical departure of vortices downstream of the flap is achieved.
The negative effect of the speed brake known from the prior art is reduced with the invention so that the durability of aircraft components arranged downstream thereof is improved and the speed brake can be deflected at a greater angle to the flow. By the extension according to the invention, neither the aircraft performance nor the strength of the speed brake is influenced.